The present invention relates to the fields of audio loudspeakers, and more particularly to a speaker suspended without a xe2x80x9cspiderxe2x80x9d or xe2x80x9csurround,xe2x80x9d wherein the motion of the speaker is controlled by an active restoring apparatus.
A representative prior art audio speaker 10 is illustrated in FIG. 1. Most speakers, like speaker 10, comprise a diaphragm 12 driven by a voice coil 14. The voice coil 14 is mounted in a magnetic field created by magnet 22. The magnet 22 is supported on a back plate 18 and has a top plate 16 and a pole piece 20 forming a magnetic assembly 23. The diaphragm 12 is supported in such a way that it is free to vibrate in a linear direction, restrained by a spring apparatus. Usually the spring apparatus takes the form of a surround 24 and a spider 26. When an audio signal is fed to the coil 14, the diaphragm 12 moves away from a neutral position. The spider 26 and surround 24 act both to constrain speaker to a linear motion and to provide a restoring force, returning the diaphragm 12 to the neutral position in the absence of a displacing force provided by the coil 14.
The spring action in the spider and surround are potentially distorting to sound reproduction, particularly where wide ranges of frequencies or amplitudes are expected. The spider and surround usually act as linear springs over most of their range of motion, coming to a relatively abrupt stop at maximum extension in either the forward or backward direction. In certain situations, particularly with high audio power and at low bass frequencies, the speaker may be driven beyond its physical constraints, striking a hard constraint or straining against the suspension at its limit, a phenomenon referred to as xe2x80x9cbottoming.xe2x80x9d Bottoming can introduce serious distortion and risk physical damage or deterioration of the speaker.
It is an object therefore, of our invention, to provide a speaker system without a spring-type suspension.
It is also an object of our invention to provide a speaker with an active restoring apparatus.
Another feature or object of our invention is to provide a speaker with a frictionless bearing, that is, negligible friction, constraint, the constraint limiting direction travel of the diaphragm to a linear direction.
The objects of our invention have been accomplished by providing a spider-less and suspension-less speaker system, having a diaphragm constrained to move in a linear direction and supported by a frictionless or low friction support. A voice coil coupled to an audio input drives the speaker diaphragm. A position sensor determines the physical position of the diaphragm. A control circuit uses the sensed position information to modify the audio signal in such a way that the interaction of the voice coil and the magnetic field both drives the diaphragm to produce an audible output and restores the diaphragm to a neutral position in the absence of a further audio signal.